This invention relates to hydraulically or pneumatically actuated muscles, that is, devices which convert a fluid pressure into a tensive force. The invention is more specifically directed to terminator or obturator structure for sealing one or both ends of an elongated bladder of the hydraulic muscle and also providing for force transfer between a tubular braid of the muscle and an anchor point or cable. For purposes of discussion, the term "muscle" is used both for a hydraulic or pneumatic actuator which converts fluid pressure to mechanical force, and for a fluid pump that converts a tensive mechanical force to a pressure.
Hydraulic muscles can be favorably employed in an elongated flexible probe such as a borescope or endoscope for actuating its articulation or steering section. With the use of hydraulic muscles, the conventional long steering cables can be eliminated. This use of a hydraulic muscle in a borescope or endoscope is described in U.S. patent application Ser. No. 357,806, filed May 30, 1989, and having a common assignee herewith. Another fluid dynamic muscle in a borescope or endoscope is described in U.S. Pat. No. 4,794,912, granted Jan. 3, 1989. Fluid dynamic articulation and steering for a borescope or endoscope offers a distinct improvement over the conventional system of steering cables, permitting much more accurate and precise positioning of the viewing end of the instrument within the cavity to be inspected.
The hydraulic, or fluid dynamic muscle is made of an elongated tubular bladder which is encased in an elongated tubular braid member disposed over it. Terminators are provided at the proximal and distal ends of the muscle to seal the ends of the bladder and to provide a place for mechanical attachment between the ends of the braid member and the mechanical members to which they are to transfer force, e.g. a cable or a muscle sheath. The braid permits the bladder within it to expand laterally when hydraulic pressure is applied to it. However, as the braid and bladder expand radially, the braid contracts axially and generates an axial tensive force.
Currently, the practice is to bind the braid and bladder down with a cord or cinch onto the terminator which is in the form of an elongated cylinder. This means that any mechanical forces transferred between the terminator and the braid member must also pass through the end of the bladder. If the device is subjected to axial forces exceeding about 20 pounds, or to an internal fluid pressure above about 100 psig, there tends to be axial slippage of the external braid and internal bladder relative to the terminator. Fluid can also leak out around the terminator under these circumstances.